1. Field of the Invention
The present invention relates to a method of a photoelectronic device for separating a semiconductor layer from a substrate, and relates more particularly to a method for separating a semiconductor from a substrate by using wet-etching process.
2. Description of the Related Art
The word epitaxy derives from a combination of two Greek words, epi (“upon”) and taxis (“ordered”), meaning that one material is arranged in an ordered manner upon another material. In the semiconductor industry, the epitaxial growth process is used during manufacture for depositing a film material upon a substrate. The epitaxial growth process is different from crystal growth by using the Czochralski process. The epitaxial growth processes can be categorized into three categories: (1) liquid phase epitaxy (LPE) process; (2) vapor phase epitaxy (VPE) process; (3) molecular beam epitaxy (MBE) process. The VPE process can be further categorized according to reaction type into (a) chemical vapor deposition (CVD) and (b) physical vapor deposition (PVD). By using the epitaxial growth process, a semiconductor film can be grown by controlling reaction parameters to have an amorphous crystal structure, a poly crystal structure or a single crystal structure, and dopants can be directly added during the process, eliminating the need for diffusion and ion implantation processes.
However, during the epitaxial process, a semiconductor layer may have lattice dislocation and thermal stress issues because the semiconductor layer and its heterosubstrate have different lattice constants and coefficients of thermal expansion. Conventionally, substrates used for eptiaxial processes usually have characteristics that are insufficient or unsuitable for the later processing steps of manufacturing an optoelectronic device or for the application of semiconductor components. Therefore, many techniques have been developed for separating semiconductor layers and attempting to solve said problem.
For example, a paper by Yablonovitch, et al. published in Appl. Phys. Lett. 51, 2222 (1987) proposes to implement AlAs sacrificial layers in the GaAs/AlAs material system during the production process, which can then be dissolved by using wet chemical means. This makes it possible to separate layers or structures from the substrate. However, because of the low lateral etching rate, this process is very time-consuming.
U.S. Pat. No. 4,448,636 describes a process for removing metal films from a substrate. First, the metal film is heated by light. An organic sacrificial layer between the substrate and the metal film is vaporized by the heat and allows the metal layer to be removed. Such organic intermediate layers cannot be employed, however, in the epitaxial growth of group III nitrides.
A comparable process has been described for removing silicon dioxide layers from gallium arsenide in Y. F. Lu, Y. Aoyagi, Jpn. J. Appl. Phys. 34, L1669 (1995). In this process, an organic intermediate layer is heated by light absorption and the SiO2 layer is lifted off.
A paper by Y. F. Lu, Y. Aoyagi, published in Jpn. J. Appl. Phys. 33, L324(1994) proposes a method that uses an Excimer laser beam to separate silicon oxide strips from a GaAs layer.
Specifically for group III nitrides, Leonard and Bedair, Appl. Phys. Lett. 68, 794 (1996) describe the etching of GaN with a laser pulse under HCl gas so as to perform a separation process.
Although many separation methods, including the above, have been introduced, such methods suffer from deficiencies such as high cost, limited availability of material required by the methods, low efficiency, and excessive destruction of semiconductor structures. Therefore, a new method is required to overcome the limitations of prior methods.